Oak Tree not looking good

Howdy, I have a huge oak tree that last year lost some leaves from one side of the canopy. I got concerned and had an arborist come out. He really didn't give me any info but did a dna test and recommended a treatment once he got the results back from the lab. I couldn't tell you what he said it was diagnosed with, but the treatment was drilling holes around the base of the tree and injecting something in it. That apparently didn't help anything because it is doing the same this year and is slightly worse. I'd love to hear opinions on here about what it is. I just hate to lose it because it's so old and beautiful.

Thanks for your reply ATH. The building was built about 13 years ago. No grade changes or water pattern changes. I do apply fertilizer to the yard, but nothing else besides that. Occasionally I will spray roundup around the shop but nothing more serious than that.

Thanks for your reply ATH. The building was built about 13 years ago. No grade changes or water pattern changes. I do apply fertilizer to the yard, but nothing else besides that. Occasionally I will spray roundup around the shop but nothing more serious than that.

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First thing I notice is no mulch island. Turf grass is not your trees friend! I'm surprised your arborist did not mention the benefits of a good organic mulch bed. Have you been experiencing droughts in the last two years ? Fertilizer what kind and application rates and yearly ?